fix: only look up the parts count when ObjectParts is requested

The controller now passes the requested attributes to the backend in
ObjectAttributes, so posix and azure only do the extra HeadObject for the
parts count when ObjectParts was asked for. This also lets the s3 backend
reach the upstream service, which rejected the request before because the
field was missing.

The s3 backend now copies TotalPartsCount into PartsCount, leaves out
ObjectParts when the upstream response has none, and sets the part number
markers, which were dropped by inverted strconv.Atoi error checks.

backend/azure/azure.go

@@ -764,22 +764,23 @@ func (az *Azure) GetObjectAttributes(ctx context.Context, input *s3.GetObjectAtt
 		return s3response.GetObjectAttributesResponse{}, err
 	}
 
-	// HeadObject reports the parts count only when a part is requested, and
-	// only for objects completed from a multipart upload
-	partNumber := int32(1)
-	part, err := az.HeadObject(ctx, &s3.HeadObjectInput{
-		Bucket:     input.Bucket,
-		Key:        input.Key,
-		PartNumber: &partNumber,
-	})
-	if err != nil {
-		return s3response.GetObjectAttributesResponse{}, err
-	}
-
 	var objParts *s3response.ObjectParts
-	if part.PartsCount != nil {
-		objParts = &s3response.ObjectParts{
-			PartsCount: part.PartsCount,
+	if slices.Contains(input.ObjectAttributes, types.ObjectAttributesObjectParts) {
+		// HeadObject reports the parts count only when a part is requested,
+		// and only for objects completed from a multipart upload
+		partNumber := int32(1)
+		part, err := az.HeadObject(ctx, &s3.HeadObjectInput{
+			Bucket:     input.Bucket,
+			Key:        input.Key,
+			PartNumber: &partNumber,
+		})
+		if err != nil {
+			return s3response.GetObjectAttributesResponse{}, err
+		}
+		if part.PartsCount != nil {
+			objParts = &s3response.ObjectParts{
+				PartsCount: part.PartsCount,
+			}
 		}
 	}
 

backend/posix/get_object_attributes_test.go

@@ -27,8 +27,8 @@ import (
 )
 
 // TestGetObjectAttributesPartsCount checks that GetObjectAttributes reports
-// the parts count of an object completed from a multipart upload, and no
-// object parts for an object that wasn't.
+// the parts count of an object completed from a multipart upload when
+// ObjectParts is requested, and no object parts for an object that wasn't.
 func TestGetObjectAttributesPartsCount(t *testing.T) {
 	for name, mkMeta := range metaModes(t) {
 		t.Run(name, func(t *testing.T) {
@@ -79,9 +79,11 @@ func TestGetObjectAttributesPartsCount(t *testing.T) {
 				t.Fatalf("complete multipart upload: %v", err)
 			}
 
+			partsAttr := []types.ObjectAttributes{types.ObjectAttributesObjectParts}
 			out, err := p.GetObjectAttributes(ctx, &s3.GetObjectAttributesInput{
-				Bucket: &bucket,
-				Key:    &mpKey,
+				Bucket:           &bucket,
+				Key:              &mpKey,
+				ObjectAttributes: partsAttr,
 			})
 			if err != nil {
 				t.Fatalf("get multipart object attributes: %v", err)
@@ -96,6 +98,19 @@ func TestGetObjectAttributesPartsCount(t *testing.T) {
 				t.Errorf("expected object size %d, got %d", totalSize, got)
 			}
 
+			// the parts count is only looked up when ObjectParts is requested
+			out, err = p.GetObjectAttributes(ctx, &s3.GetObjectAttributesInput{
+				Bucket:           &bucket,
+				Key:              &mpKey,
+				ObjectAttributes: []types.ObjectAttributes{types.ObjectAttributesObjectSize},
+			})
+			if err != nil {
+				t.Fatalf("get multipart object size: %v", err)
+			}
+			if out.ObjectParts != nil {
+				t.Errorf("expected no object parts when not requested, got %+v", *out.ObjectParts)
+			}
+
 			key := "obj"
 			_, err = p.PutObject(ctx, s3response.PutObjectInput{
 				Bucket:        &bucket,
@@ -108,8 +123,9 @@ func TestGetObjectAttributesPartsCount(t *testing.T) {
 			}
 
 			out, err = p.GetObjectAttributes(ctx, &s3.GetObjectAttributesInput{
-				Bucket: &bucket,
-				Key:    &key,
+				Bucket:           &bucket,
+				Key:              &key,
+				ObjectAttributes: partsAttr,
 			})
 			if err != nil {
 				t.Fatalf("get object attributes: %v", err)

backend/posix/posix.go

@@ -6451,23 +6451,24 @@ func (p *Posix) GetObjectAttributes(ctx context.Context, input *s3.GetObjectAttr
 		return s3response.GetObjectAttributesResponse{}, err
 	}
 
-	// HeadObject reports the parts count only when a part is requested, and
-	// only for objects completed from a multipart upload
-	partNumber := int32(1)
-	part, err := p.HeadObject(withCtxNoSlot(ctx), &s3.HeadObjectInput{
-		Bucket:     input.Bucket,
-		Key:        input.Key,
-		VersionId:  input.VersionId,
-		PartNumber: &partNumber,
-	})
-	if err != nil {
-		return s3response.GetObjectAttributesResponse{}, err
-	}
-
 	var objParts *s3response.ObjectParts
-	if part.PartsCount != nil {
-		objParts = &s3response.ObjectParts{
-			PartsCount: part.PartsCount,
+	if slices.Contains(input.ObjectAttributes, types.ObjectAttributesObjectParts) {
+		// HeadObject reports the parts count only when a part is requested,
+		// and only for objects completed from a multipart upload
+		partNumber := int32(1)
+		part, err := p.HeadObject(withCtxNoSlot(ctx), &s3.HeadObjectInput{
+			Bucket:     input.Bucket,
+			Key:        input.Key,
+			VersionId:  input.VersionId,
+			PartNumber: &partNumber,
+		})
+		if err != nil {
+			return s3response.GetObjectAttributesResponse{}, err
+		}
+		if part.PartsCount != nil {
+			objParts = &s3response.ObjectParts{
+				PartsCount: part.PartsCount,
+			}
 		}
 	}
 

backend/s3proxy/s3.go

@@ -1222,27 +1222,23 @@ func (s *S3Proxy) GetObjectAttributes(ctx context.Context, input *s3.GetObjectAt
 		return s3response.GetObjectAttributesResponse{}, handleError(err)
 	}
 
-	parts := s3response.ObjectParts{}
-	objParts := out.ObjectParts
-	if objParts != nil {
+	var parts *s3response.ObjectParts
+	if objParts := out.ObjectParts; objParts != nil {
+		parts = &s3response.ObjectParts{
+			Parts:      objParts.Parts,
+			PartsCount: objParts.TotalPartsCount,
+		}
 		if objParts.PartNumberMarker != nil {
-			partNumberMarker, err := strconv.Atoi(*objParts.PartNumberMarker)
-			if err != nil {
-				parts.PartNumberMarker = partNumberMarker
-			}
-			if objParts.NextPartNumberMarker != nil {
-				nextPartNumberMarker, err := strconv.Atoi(*objParts.NextPartNumberMarker)
-				if err != nil {
-					parts.NextPartNumberMarker = nextPartNumberMarker
-				}
-			}
-			if objParts.IsTruncated != nil {
-				parts.IsTruncated = *objParts.IsTruncated
-			}
-			if objParts.MaxParts != nil {
-				parts.MaxParts = int(*objParts.MaxParts)
-			}
-			parts.Parts = objParts.Parts
+			parts.PartNumberMarker, _ = strconv.Atoi(*objParts.PartNumberMarker)
+		}
+		if objParts.NextPartNumberMarker != nil {
+			parts.NextPartNumberMarker, _ = strconv.Atoi(*objParts.NextPartNumberMarker)
+		}
+		if objParts.MaxParts != nil {
+			parts.MaxParts = int(*objParts.MaxParts)
+		}
+		if objParts.IsTruncated != nil {
+			parts.IsTruncated = *objParts.IsTruncated
 		}
 	}
 
@@ -1251,7 +1247,7 @@ func (s *S3Proxy) GetObjectAttributes(ctx context.Context, input *s3.GetObjectAt
 		LastModified: out.LastModified,
 		ObjectSize:   out.ObjectSize,
 		StorageClass: out.StorageClass,
-		ObjectParts:  &parts,
+		ObjectParts:  parts,
 		Checksum:     out.Checksum,
 	}, nil
 }

s3api/controllers/object-get.go

@@ -388,8 +388,14 @@ func (c S3ApiController) GetObjectAttributes(ctx fiber.Ctx) (*Response, error) {
 		}, err
 	}
 
+	objAttrs := make([]types.ObjectAttributes, 0, len(attrs))
+	for attr := range attrs {
+		objAttrs = append(objAttrs, types.ObjectAttributes(attr))
+	}
+
 	res, err := c.be.GetObjectAttributes(ctx.RequestCtx(),
 		&s3.GetObjectAttributesInput{
+			ObjectAttributes:     objAttrs,
 			SSECustomerAlgorithm: ssec.Algorithm,
 			SSECustomerKey:       ssec.Key,
 			SSECustomerKeyMD5:    ssec.KeyMD5,